Shape memory alloy actuator

Abstract

A shape memory alloy (SMA) actuator for engaging and actuating a device. The actuator includes an engagement mechanism, a bias element, and a SMA object(s). The SMA actuator may automatically and passively transfer to a backup or redundant feature that resets or extends the actuator's operational life. In one embodiment, the SMA actuator includes an additional SMA object(s) that replaces the primary SMA object(s) in the event the primary SMA object(s) breaks. The SMA actuator may also be configured to apply a dynamic stress to the SMA object during transition of the object to modify the transition temperatures of the object. The SMA actuator may be part of a fluid distribution system, such as a heating, ventilation, and air conditioning (HVAC) system and used to control the flow of fluid, such as air, from the distribution system.

1. A shape memory alloy actuator, comprising:
 a first shape memory alloy object and a second shape memory alloy object; 
 a movable member to which the first shape memory alloy object and a second shape memory alloy object attach; 
 the movable member being movable between a first position and a second position; 
 a bias element attached to the movable member, wherein the bias element applies a stress to the first shape memory alloy object when the movable member is in the first position and applies a stress to the second shape memory alloy object when the movable member is in the second position, wherein in the first position the second shape memory alloy object is not subject to stress from the bias element and in the second position the first shape memory alloy object is not subject to stress from the bias element; and 
 the bias element is generally coaxial with the first shape memory alloy object when the movable member is in the first position and generally coaxially with the second shape memory alloy object when the movable member is in the second position. 
 
     
     
       2. The shape memory alloy actuator of  claim 1  wherein the movable member automatically moves from the first position to the second position when the first shape memory alloy object fails. 
     
     
       3. The shape memory alloy actuator of  claim 1  further comprises a bracket, wherein the first shape memory alloy object has a first end that is attached to the bracket and a second end that is attached to the movable member and the second shape memory alloy object has a first end that is attached to the bracket and a second end that is attached to the movable member. 
     
     
       4. The shape memory alloy actuator of  claim 3  wherein the bias element has a first end that is attached to the bracket and a second end that is attached to the movable member. 
     
     
       5. The shape memory alloy actuator of  claim 4  wherein the bracket has a plurality of locations adapted to connect to the first end of the bias element. 
     
     
       6. The shape memory alloy actuator of  claim 3  wherein the movable member is rotatable relative to the bracket and axially movable relative to the bracket. 
     
     
       7. The shape memory alloy actuator of  claim 1  further comprising a lever pivotally attached to a housing and movable between a first lever position and a second lever position, the lever having a first end attached to the movable member. 
     
     
       8. The shape memory alloy actuator of  claim 6  wherein when the movable member is in the first position, the first shape memory alloy object contracts as a function of temperature to move the pivotal lever from the second lever position to the first lever position. 
     
     
       9. The shape memory alloy actuator of  claim 8  wherein the stress on the first shape memory alloy object decreases as the first shape memory alloy object contracts. 
     
     
       10. The shape memory alloy actuator of  claim 6  wherein the bias element biases the pivotal lever toward the second lever position. 
     
     
       11. A shape memory alloy actuator, comprising:
 a first shape memory alloy wire and a second shape memory alloy wire, wherein each shape memory alloy wire includes a first fixed end and a second end; 
 a cam to which the second end of the first shape memory alloy wire and the second end of the second shape memory alloy wire attach, the cam being rotatable between a primary position and secondary position; and 
 a bias element attached to the cam such that the bias element applies a stress to the first shape memory alloy wire in the primary position and applies a stress to the second shape memory alloy wire in the secondary position, the bias element is generally coaxial with the first shape memory alloy wire when the cam is in the primary position and generally coaxially with the second shape memory alloy wire when the cam is in the secondary position; and 
 a lever attached to the movable member and pivotable about an axis,wherein each shape memory alloy wire is capable of expanding and contracting as a function of temperature such that when the shape memory alloy wire being stressed contracts, the lever moves to a first lever position and when the shape memory alloy being stressed expands, the lever moves to a second lever position. 
 
     
     
       12. The shape memory alloy actuator of  claim 11  wherein when the cam is in the primary position, the second shape memory alloy wire is not subject to stress from the bias element. 
     
     
       13. The shape memory alloy actuator of  claim 11  wherein the cam automatically moves from the primary position to the secondary position when the first shape memory alloy wire fails. 
     
     
       14. A diffuser for a fluid distribution system, comprising a housing;
 a blade assembly pivotally mounted within the housing and movable between a first position and a second position; 
 a blade actuator, comprising a bias element adapted to move the blade assembly from the first position to the second position; 
 a first shape memory alloy object adapted to move the blade assembly from the second position to the first position against the bias of the bias element when the first shape memory alloy object is in an active position; 
 a second shape memory alloy object adapted to move the blade assembly from the second position to the first position against the bias of the bias element when the second shape memory alloy object is in an active position, wherein the second shape memory alloy object is not subject to the bias force from the bias element when the first shape memory alloy object is in an active position. 
 
     
     
       15. The diffuser of  claim 14  wherein second shape memory alloy object automatically transitions to an active position when the first shape memory alloy object fails. 
     
     
       16. The diffuser of  claim 14  further comprising a movable member to which the bias element, the first shape memory alloy object, and the second shape memory alloy object attach. 
     
     
       17. The diffuser of  claim 14  wherein the blade actuator is mounted within the housing. 
     
     
       18. The diffuser of  claim 14  wherein the blade actuator further comprises a pivotal lever having a first end attached to the movable member and a second end adapted to engage the blade assembly. 
     
     
       19. The diffuser of  claim 14  wherein the first shape memory alloy object is generally coaxial with the bias element when the first shape memory alloy object is the active position, and wherein the second shape memory alloy object moves to a position that is generally coaxially with the bias element when the second shape memory alloy object moves from an inactive position to an active position. 
     
     
       20. The diffuser of  claim 14  wherein the housing further comprises a fluid inlet and a fluid outlet, and wherein fluid flowing from the fluid inlet to the fluid outlet applies a force to the blade assembly that reduces the stress load on the shape memory alloy wire in the active position as the shape memory alloy wire moves the blade assembly from the second position to the first position. 
     
     
       21. A diffuser for a fluid distribution system, comprising a housing;
 a blade assembly pivotally mounted within the housing and movable between a first blade position and a second blade position; 
 a blade actuator mounted within the housing, the blade actuator, comprising a bias element adapted to move the blade assembly from the first blade position to the second blade position; 
 a first shape memory alloy object adapted to move the blade assembly from the second blade position to the first blade position against the bias of the bias element when the first shape memory alloy object is in an active position, wherein the first shape memory alloy object is generally coaxial with the bias element when the first shape memory alloy object is the active position; 
 a second shape memory alloy object adapted to move the blade assembly from the second blade position to the first position against the bias of the bias element when the second shape memory alloy object is in an active position, wherein the second shape memory alloy object is not subject to the bias force from the bias element when the first shape memory alloy object is in an active position, and wherein the second shape memory alloy object moves to a position that is generally coaxially with the bias element when the second shape memory alloy object moves from an inactive position to an active position; and 
 a movable member to which the bias element, the first shape memory alloy object, and the second shape memory alloy object attach, the movable member adapted to automatically move the second shape memory alloy object from the inactive position to the active position when the first shape memory alloy object fails.